In a new survey, most women had inaccurate perceptions about the safety and effectiveness of intrauterine devices (IUDs) in preventing pregnancy, say U.S. researchers, who urge doctors to talk more about the benefits of the devices.

In particular, many of the study participants didn't know that IUDs are more effective contraceptives than the birth control pill and that the devices don't increase the risk of getting a sexually transmitted disease.

"It's not clear whether women have an overly optimistic view of the effectiveness of the birth control pill or an overly pessimistic view of the IUD," said Dr. Lisa Callegari, the study's lead author and a clinical assistant professor at the University of Washington.

Whatever their source, these misperceptions lead to underuse of "one of the most safe and effective methods" of birth control, said Dr. Jeffrey Peipert, an obstetrics and gynecology professor at Washington University, who was not part of the study.

IUDs, which include the brand name products ParaGard and Mirena, are small plastic or copper-and-plastic objects inserted into the uterus. They can be left implanted for years, and are more than 99 percent effective at preventing pregnancy.

In contrast, the birth control pill has been found in real-world practice to be about 95 percent effective.

Callegari said that earlier studies have highlighted some of the mistaken beliefs women have about IUDs, and she and her colleagues wanted to get a better sense of how common they are among average women visiting primary care clinics.

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They surveyed more than 1,600 women between the ages of 18 and 50 who had visited one of four clinics in Pennsylvania.

Five percent of the women were currently using an IUD, and another 5.8 percent had used one previously.

Only about one in five of the women correctly stated that IUDs are more effective at preventing pregnancy than the Pill.

And just 28 percent knew that an IUD is more cost effective than the Pill when it is used for more than three years, the researchers report in the medical journal Contraception.

According to Planned Parenthood, the upfront costs of an IUD are between $500 and $1,000, whereas birth control pills can cost between $15 and $50 a month - so they become more expensive over time.

The women in the study were considerably more knowledgeable about the risk of disease related to an IUD, with 57 percent answering correctly that there is no greater risk of contracting a sexually transmitted disease with an IUD compared to the Pill.

Still, Peipert said he's not surprised that women might view IUDs less favorably.

"There's been a LOT of bad press about IUDs in the past," Peipert wrote in an email to Reuters Health.

For instance, thousands of women have sued the makers of the Dalkon Shield, an IUD sold in the 1970s, because of injuries sustained from infections.

"It's not surprising, because of the history of the IUD in the United States, that people still have inaccurate perceptions of the device," said Dr. Rebecca Allen, an assistant professor of obstetrics and gynecology at Brown University, who was not involved in the study.

Currently available devices are considered to be much safer, said Allen.

Indeed, women over age 36 tended to have more misperceptions than younger women who took the survey, the researchers note in their report.

It's likely, too, that many women are simply not as familiar with the devices as they are with the Pill, said Callegari.

According to a 2012 study by the Centers for Disease Control and Prevention (CDC), 28 percent of women of reproductive age use oral contraception, making the Pill the most common form of birth control, followed closely by sterilization methods like getting the fallopian tubes "tied," used by 27 percent of women.

The same CDC study found that IUD use had risen from 0.8 percent of reproductive-age women in 1995 to 5.6 percent in 2010.

To correct widespread misconceptions about IUDs, Allen said, health care providers should be encouraged to talk to their patients about the devices.

Among women who have never used an IUD, Callagari's study found that those who had been counseled about the device by a health care provider were more knowledgeable than women who hadn't discussed it.

"I think it helps to give more evidence that providers should be talking with patients about IUDs," she told Reuters Health. "Women hear it and it affects their perceptions."

Providers themselves might need to be educated too, however.

One recent survey of physicians found that 30 percent had outdated ideas about IUDs, including thinking they are unsafe for women who had never had a baby or being unsure about their safety.

"We need to educate more primary care providers about the facts about IUDs so that they can counsel their patients," said Allen.